namespace Library
{
   public interface IReader
   {
      char Read();
   }
   public interface IWriter
   {
      void Write(char c);
   }
   public class Copier
   {
      public static IReader Reader = new NullImpl();
      public static IWriter Writer = new NullImpl();

      public static void Copy()
      {
         char c;
         while ((c = Reader.Read()) != 'x')
            Writer.Write(c);
      }


      private class NullImpl : IReader, IWriter
      {
         public char Read()
         {
            return 'x';
         }
         public void Write(char c)
         {
         }
      }
   }
}